Electromagnetic vibratory unit



Jan. 3, 1961 J. F. WAHL 2,967,253

ELECTROMAGNETIC VIBRATORY UNIT Filed May 12, 1958 INVENTOR.

John F Wa'hZ BY gfiz My 0146 m V Qiiarneys Patented Jan. 3, 1961 @fiieeELECTROMAGNETKC VIBRATGRY UNIT John F. Wahl, Sterling, Ili., assignor toWahl Clipper Corporation, Sterling, Ill., a corporation of lilinoisFiled May 12, M58, Ser. No. 734,605

4 Claims. (Cl. 310-29) This invention relates to an electromagneticvibratory unit, and more particularly to an armature assembly for anelectromagnetic vibratory unit which operates so that its powerconsumption and its power output do not de crease appreciably withincrease of load.

As increasing load is applied to a conventional alternating currentelectromagnetic vibratory unit, the stroke length of the magneticarmature will decrease. Since the power consumption, and consequentlythe power output of such vibratory units varies in accordance withmagnetic armature stroke length, it has been found that when the load inthe conventional vibratory unit is increased to where the magneticarmature is stopped completely, i.e. a stalling condition, then thepower input to the motor drops by at least 25%. So if a conventionalmotor or vibrating unit draws 8 watts, for example, when operating underno load, then it will draw about 6 watts in a stalling condition, and asthe vibratory unit ap proaches this stalling condition, its power outputand the stroke length of the magnetic armature will decreaseproportionately.

The foregoing means, for example, that if load conditions should requirea power output of 8 watts, then a conventional vibratory unit would haveto be selected which draws from 10 to 12 watts under no load conditions.This is a most inefficient arrangement both because the conventionalvibratory units draw the greatest quantity of power when they least needit, i.e. under no load conditions, and because larger and more expensive units are required for a given load than would otherwise benecessary if their power consumption did not armature assembly can beselected so that the stroke of the magnetic armature will not decreasesubstantially under load. As a matter of fact, if the spring constantsof the armature system are chosen properly, the stroke of the magneticarmature may even remain constant or increase slightly as load isapplied to the vibrating unit.

As seen in the drawings, the principles of this invention are embodiedin a vibratory motor for a hair clipper, but it is evident that theseprinciples could be applied to a large variety of different kinds ofvibrating units. What is needed therefore, and comprises the principleobject of this invention is an electromagnetic vibratory unit which isdesigned so its power consumption and power output will not decreaseappreciably with load. Another object of this invention is to provide anelectromagnetic vibratory unit in which the stroke length of themagnetic armature under any load condition is never less than one-thirdits stroke length under no load condition.

These and other objects of this invention will become apparent when readin the light of the accompanying drawings and specifications.

In the drawing:

Fig. 1 is a plan view of a hair clipper with a portion of the casingbroken away to show an armature assembly embodying the principles ofthis invention.

Fig. 2 is a side view of the hair clipper of Fig. 1 with a portion ofthe casing broken away to show another view of the armature assembly.

Fig. 3 is an enlarged plan view of a portion of the armature assemblyalone showing the shape of the magnetic armature and one form ofresilient work arm which connects to a movable cutting blade.

Referring now to Fig. l of the drawing, a hair clipper embodying thenovel features of this invention and indicated generally by thereference numeral 10 comprises casing 12 and a fixed cutter blade 14which is secured to the casing by means such as bolt 15, see Fig. 2.

An electromagnetic coil 16 is rigidly secured to casing 12. An armatureassembly 18, comprising a magnetic armature'2il and a vibratoryresilient overtuned part is also secured to the casing at end portion19. The resilient overtuned part comprises a resilient work arm 22, amounting 24, and the work contacting portion or cutter blade 26. As seenin the drawings, the resilient work arm 22 is connected to the end ofthe magnetic armature 2d, and the mounting 24 and the movable cutterblade 26 are secured to the free end 23 of the resilient work arm 22.The resilient work arm 22 is connected at or near the free end of themagnetic armature to give it substantial travel. With this arrangementvibrations of the magnetic armature 2i) drive the movable cutter blade26. The fixed and movable cutter blades 14 and 26, as seen in Fig. 2slide against each other in the usual manner. As will be understood, themagnetic armature 2t) vibrates in accordance with the varying magneticfield produced by the electromagnetic coil 16.

A conventional armature assembly, adjusting screw 28, shown in Fig. 1,is provided for adjusting the size of air gap 21 between a pole 25 ofcoil 16 and magnetic armature 2d.

The constructions thus far described, except for the resilient Work arm22, are relatively conventional. Heretofore, in conventional clippers,the connection between the end of the magnetic armature and the movablecutter blade was comparatively rigid, insofar as relative movementsbetween the end of the armature and the movable cutter blade in theplane of their vibratory movements was concerned. It is important tonote, however, that even in conventional clippers a ditferent kind ofresilient connection between the magnetic armature and the movablecutter blade usually is provided. This conventional resilient connectionand the consequent relative movement is illustrated by the arcuatearrows in Fig. 2, and this resilience provides cutting bias between theblades and enables the blades to stay properly in cutting relation.

In this invention, however, resilience between the magnetic armature andthe movable cutter blade refers only to a -esilience which permitsrelative movements between the magnetic armature and the movable cutterblade in the plane of their vibratory movements. This is illustrated bythe straight arrows in Fig. 3. Without such a resilient connection, itcan be seen that if movable cut ter blade 26 is slowed by heavy loads,then the stroke of magnetic armature 2 will decrease, resulting, asindicat ed above, in a decrease in the power output of the motor.

The limitations on resilient work arm 22 are very severe. It is apparentfrom an inspection of Fig. 3, that if the resilience of the work arm istoo great, then any load can stop the movement of movable cutter blade26 regardless of the movement of magnetic armature 26. It is alsoundesirable for the resilience to be such that the work arm isunder-tuned because an objectionable phase shift between the movement ofthe cutter blade 26 and the armature 20 would be introduced. On theother hand, if the resilience in the work arm is too small, heavy loadson the vibratory unit could cause a substantial decrease in the strokeof the magnetic armature, and consequently cause the power output of theunit to drop. The unit in this case would operate much the same asconventional units.

Ideally it would be desirable for the resilient work arm to affect thearmature assembly so that there either is no decrease in the stroke ofthe magnetic armature under load or else that the stroke will actuallyincrease. Too large an increase in the stroke of the magnetic armaturein the illustrated embodiment is, however. undesirable as the armaturetends to strike against pole 25. Despite the ideal operating conditionsdescribed above, even if the magnetic armature stroke length decreasedby as much as two-thirds under. loads heavy enough to stall the movablecutter blade, this improved vibratory unit would be superior toconventional vibratory units where the magnetic armature issubstantially motionless at a stalling load.

In this device, advantage is taken of the behavior of the illustratedvibrating spring system when it encounters a load in the form ofresistance to movement. The effect of such a load on the vibratingspring system acts to increase the spring constant of the armatureassembly. This in turn causes the tune or natural frequency of thearmature assembly to increase. If this increase in the natural frequencyof the armature assembly is towards the frequency of the applied force,i.e. resonance, the amplitude of vibration of the armature assemblywould tend to increase. and this is desirable. This means that thearmature assembly must be undertuned.

For this to occur, it is evident that the tune of the armature assemblywould have to be below 120 cycles per second since the frequency of theapplied force when a 60 cycle current is applied to the electromagneticcoil is 120 cycles per second. With this arrangement if a load isapplied to the armature assembly of such a vibrating unit, then the tuneof the armature assembly increases toward resonance, and consequentlythe stroke of the magnetic armature will tend to increase.

In this vibratory unit the armature assembly is designed so it isundertuned under no load condition (at least 20% undertuned has beenfound most desirable, i.e. 95 to 105 cycles). Despite the fact that theannature assembly is undertuned, the resilient work arm and associatedload device (blade) taken alone must be overtuned, i.e., having anatural frequency or tune of over 120 cycles per second. The extent ofovertuning of the work arm-blade assembly is dependent upon therelationship between the momentnms of the armature arm and the workarm-blade assembly. A relatively light work arm-blade assembly connectedto a heavy magnetic armature will cause a moderate rise in the naturaltune of the armature assembly under load. Conversely, a. relativelyheavy work arm-blade assembly having the same extent of overtuningconnected to a light magnetic armature will cause a substantiallygreater rise in the natural tune of the armature assembly under load. Itcan be seen that by making suitable selections in the masses and lengthsof portions of the armature assembly, the character of the increase inthe tune of the armature assembly can be controlled.

At no load, since the work arm-blade assembly is overtuned itsresilience will have no effect on the amplitude of the magneticarmature. As load is applied to the 4 vibrating unit, the tune of theentire armature assembly will increase towards resonance, and as long assuch tune is less than over resonance when a blade stalling load isreached, the flexibility of resilient work arm 22 will cause the strokelength of the magnetic armature under any blade load to remain within atleast one-third of its stroke length under no load conditions. Inaddition, depending upon the relative values of the spring constants ofthe magnetic armature and the resilient work arm, the stroke length ofthe magnetic armature could either be kept constant or even be permittedto increase slightly as load is applied to the unit. In this way, theabove described decrease in the power output under load conditions ofconventional vibratory units can be eliminated.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof as set forth in the claims,and the present em bodiment is therefore to be considered asillustrative and not restrictive and it is intended to include allchanges which come within the scope and range of the claims.

From the above description it is thought that the construction andadvantages of this invention will be readily apparent to those skilledin the art. Various changes in detail may be made without departing fromthe spirit or losing the advantages of the invention.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent is:

1. A vibratory motor comprising a support, a coil energized by a currentof fixed frequency mounted on said support, a magnetic circuitassociated with said coil, a resilient armature assembly connected tosaid support and movable back and forth in said magnetic circuit inresponse to the frequency of the driving force caused by the varyingmagnetic field, said armature assembly including a magnetic armature anda vibratory resilient worn arm including a work contacting portion, saidresilient work arm having a natural frequency higher than the frequencyof the driving force connected to said magnetic armature, the resilienceof said armature assembly selected so the natural frequency of thearmature assembly is below the frequency of the driving force underno-load conditions while at stalling loads on said work contactingportion the natural frequency of the armature assembly is less than 50%above the frequency of the driving force whereby the resilience of thework arm will allow the length of the stroke of the magnetic armature atany load to be at least one-third the length of its stroke at no load.

2. The apparatus described in claim 1 wherein the natural frequency ofthe armature assembly is at least 20% below the frequency of the drivingforce under no load conditions, so that the power consumption of themotor will be low under no-load conditions.

3. The apparatus described in claim 1 wherein said resilient work arm isconnected to the magnetic armature at a point having substantial travel.

4. The apparatus described in claim 3 wherein the length of the strokeof the armature increases under load so the power output of the motor isincreased.

References Cited in the file of this patent UNITED STATES PATENTS

